Mediawiki is a popular wiki. Running it has it's problems, but here we list examples of wiki's that use Mediawiki software other than xx.wikipedia.org:
* Hacteria - hackteria.org 
* P2P Foundation wiki - p2pfoundation.net
One reason to list these sites is because they can if the out-of-the-box Mediawiki API is still active, they can usually be exposed to work with the Fedwiki Mediawiki Transport to import content.
The MediaWiki web API is a web service that provides convenient access to wiki features, data, and meta-data over HTTP. - mediawiki.org
The mediawiki-transport is a single controller that implements many individual tranport features. It is a work in progress.